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<div class="section" id="boost-mpl-assert-relation">
<h1><a class="toc-backref" href="./asserts.html#id1591">BOOST_MPL_ASSERT_RELATION</a></h1>
<div class="section" id="id1308">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
#define <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, relation, y ) \
    <em>unspecified token sequence</em> \
/**/
</pre>
</div>
<div class="section" id="id1309">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>A specialized assertion macro for checking numerical conditions. Generates
a compilation error when the condition <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">relation</span> <span class="pre">y</span> <span class="pre">)</span></tt>
doesn't hold.</p>
</div>
<div class="section" id="id1310">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
</pre>
</div>
<div class="section" id="id1311">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="docutils table">
<colgroup>
<col width="15%" />
<col width="36%" />
<col width="48%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">x</span></tt></td>
<td>An integral constant</td>
<td>Left operand of the checked relation.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">y</span></tt></td>
<td>An integral constant</td>
<td>Right operand of the checked relation.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">relation</span></tt></td>
<td>A C++ operator token</td>
<td>An operator token for the relation being
checked.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1312">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any integral constants <tt class="literal"><span class="pre">x</span></tt>, <tt class="literal"><span class="pre">y</span></tt> and a legal C++ operator token <tt class="literal"><span class="pre">op</span></tt>:</p>
<pre class="literal-block">
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, op, y );
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">None.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Generates a compilation error if <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">op</span> <span class="pre">y</span> <span class="pre">)</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
has no effect.</p>
<p>When possible within the compiler's diagnostic capabilities,
the error message will include a name of the relation being checked,
the actual values of both operands, and have a general form of:</p>
<pre class="last literal-block">
<em>...</em> ************<em>...</em>assert_relation&lt;op, x, y&gt;::************) <em>...</em>
</pre>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1313">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
template&lt; typename T, typename U &gt; struct my
{
    // ...
    <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( sizeof(T), &lt;, sizeof(U) );
};

my&lt;char[50],char[10]&gt; test;

// In instantiation of `my&lt;char[50], char[10]&gt;':
//   instantiated from here
// conversion from `
//   mpl_::failed************mpl_::assert_relation&lt;<a href="./less.html" class="identifier">less</a>, 50, 10&gt;::************'
//   to non-scalar type `mpl_::assert&lt;false&gt;' requested
</pre>
</div>
<div class="section" id="id1314">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./asserts.html">Asserts</a>, <a class="reference internal" href="./assert.html">BOOST_MPL_ASSERT</a>, <a class="reference internal" href="./assert-not.html">BOOST_MPL_ASSERT_NOT</a>, <a class="reference internal" href="./assert-msg.html">BOOST_MPL_ASSERT_MSG</a></p>
</div>
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